Judge(s)/Court Below: Scalia, J., announced the judgment of the Court and delivered an opinion, Parts I and II of which were for the Court. Roberts, C. J., and Kennedy, J., joined that opinion in full; Thomas and Alito, JJ., joined as to Parts I, II–A, and II–B–1; and Ginsburg, Breyer, Sotomayor,and Kagan, JJ., joined as to Part II–B–2. Breyer J., filed an opinion concurring in part and dissenting in part, in which Ginsburg, Sotomayor, and Kagan, JJ., joined. Alito, J., filed an opinion concurring in part and dissenting in part, in which Thomas, J., joined.

EPA cannot treat greenhouse gases under the Clean Air Act as a pollutant, unless the source is required to obtain a permit because it emits other pollutants.

Respondent, the Environmental Protection Agency (EPA), developed greenhouse-gas emission standards for new motor vehicles in order to comply with the Clean Air Act and the Prevention of Significant Deterioration ("PSD") provisions. Petitioners, multiple organizations and agencies, filed for review in the D.C. Circuit Court challenging Respondent’s actions. The Court of Appeals dismissed some of the petitions for lack of jurisdiction and denied the remainder.

The Supreme Court affirmed in part and reversed in part, holding that the Clean Air Act does not compel Respondent to require a source to obtain a PSD or Title V permit. The Court reasoned that reading the phrase “air pollutant” in the PSD or Title V provisions to take on the broad meaning found in the general definitions of the Act would cause an unnecessary and impermissible revision of clear statutory terms and enormous expansion of regulatory authority without clear congressional authorization. The Court also held that Respondent reasonably interpreted the Clean Air Act to require those sources that were emitting other pollutants to obtain permits. These sources also would need to comply with “best available control technology” (BACT) for greenhouse gasses.